Thermionic device



Oct. 27, 1936. K. STEIMEL THERMIONIC DEVICE Filed Jan. 8, 1934 INVENTOR KARL. STE/MEL 1%2 ATTORNEY Patented Oct. 27, 1936 UNITED STATES PATENT OFFEQE THERMIONIC DEVICE Germany Application January 8, 1934, Serial No. 705,673 In Germany January 9, 1933 14 Claims.

This invention relates in general to thermionic devices and particularly to the structural arrangement herein.

Many difficulties are experienced in constructing multi-electrode tubes, as among others the following requirements are to be met: stability to mechanical vibrations and shocks, long surface leakage paths between the electrodes and a small inter-electrode capacity.

The primary object of the present invention is to accomplish the forementioned demands. Other advantages will become apparent, if the specification is perused in connection with the accompanying drawing.

The aim of electrode supports consists in carrying the electrodes as well as in securing the spaces between the electrodes. In addition the electrical properties have to meet certain demands. Especially the insulation resistance between the electrodes has to be high, the path for surface leakage currents as long as possible and the additional capacity between the electrodes, which is caused by the supporting elements extremely small. To meet these requirements it is necessary not only to choose a suitable form of the supporting elements, but likewise suitable materials. The difficulties increase with the number of the electrodes to be supported: the interelectrode spaces are to be observed most carefully and as the spaces are in general very small, in order to minimize the overall dimensions of the electrode system despite the augmented number of electrodes, the requirements regarding the electrical properties are hardly to be met.

In order to secure the proper distance or spacing between the electrodes it is necessary, to fix the-ends of the supports carrying the electrodes by suitable spacing members which consist of an insulating material, e. g. glass, mica or ceramic substances, and have heretofore been designed in such a manner, that a single insulating body, having the form of a disc or a rod, hold together all the supporting wires.

The arrangement according to the present invention differs from the prior art in providing two insulating spacers, each of them holding a part of the supporting wires. For instance an outer group of electrodes is held by a frame-shaped insulating piece, whereas an inner group is connected by a discor rod-shaped insulating body.

Another object of the present invention is to minimize the inter-electrode capacity. There are tubes well known in the art, which contain a screen grid in order to shield the control grid from the anode. Furthermore it is known, to

lead out either the anode or the control grid on the top side of the glass bulb, whereas the connecting wires to the other electrodes are sealed into the press. It has been proposed to perfect the shielding effect by making the screen grid longer than the other electrodes. The demands for an efficient screening or in other words for the reduction of the capacity between the control grid and the electrodes situated beyond the screen grid are particularly great, if the tube contains many electrodes and the space current is to be controlled by several electrodes according different and independent functions. As multigrid tubes of this kindhave steep characteristic curves, the control grid it to be utmost efficiently shielded from the other electrodes maintained on an alternating potential.

According'to'the present invention an arrangement is obtained, whereby a perfect screening of the control electrode from the following electrodes in tubes'containing four and more grids is accomplished and the capacity between the anode and the control electrode is reduced to a small amount, e. g. 10' cm.

For this reason the connecting wire to either the anode or the control grid is led through the top of'the evacuated vessel and an additional screen element is arranged in such a way, that both, the connecting wire and the face of the electrodes situated within the screen are shielded from the outer electrodes. The screen preferably is maintained on a constant potential, e. g. by connecting it to the cathode.

Furthermore it-has been found important, that the screen does not form a direct prolongation of the screen grid but protrudes into the space between the electrodes. The favorable eifect of this measure may be explained by the fact, that the path ofthe stray flux between the control electrode and the electrodes situated beyond the screen grid is lengthened and the effective capacity is reduced.

In addition it seems to be of advantage, to provide a similar screen element on the other end of the electrode system adjacent the press. As there is no connecting Wire to the control grid or the anode respectively on this side, the screen element may be shorter. Preferably the both screen elements are connected together and are maintained on the same constant potential.

If the connecting wire to the control grid is led through the press, it is advisable, to pay attention to the distribution and sequence of the leading-in wires and socket prongs so that a large capacity between the control grid and the other electrodes is avoided.

The invention will be more fully understood by reference to the accompanying drawing.

Fig. 1 shows the electrode system comprising an indirectly heated cathode K, four grid electrodes G1 to G4 and an anode or plate A. For the purpose of exact centering distance or spacing elements are provided on both sides. In more simple systems the lower distance piece may be simplified or even omitted. The distance pieces or spacers consist of upper and lower annular plates P1 and upper and lower circular discs P2. The supporting wires carrying the electrodes G3 and G4 and A are fixed in the annular or ringshaped plates P1, while the other electrodes, K1 G1 and G2, are fastened in suitable holes in the discs P2. The spacers P1 and P2 positioned at the same end of the electrode system are depicted in differrent planes, but they may be situated in the same plane as well. The insulating pieces or spacers P1 and P: at the upper end are connected by a metal element S, whereas the insulating pieces or spacers P1 and P2 at the lower end are connected by a metal element S1, both said elements S and S1 acting as electrostatic screens or shields. In the system now in question the screens serve to shield the grid G1 from all electrodes situated beyond the next grid G2. As it is seen, the screens are situated not only outside the electrode system, but partly protrude into the space between the electrodes, in order to lengthen the path of the stray flux.

Fig. 2 shows a similar electrode system, where the ring-shaped insulating spacers P1 are situated outside the disc-shaped plates P2, which hold the inner group of electrodes.

By the construction described above manifold advantages are obtained. At first it is possible to manufacture the distance pieces or spacers from different materials. For instance the outer ring may consist of mica and the inner plate of a ceramic material. As the holes, which accommodate the supporting wires, are situated in close proximity in the inner part, mica is not allowable for this part, as the holes may be not arranged with sufiicient precision. On the other hand it is not recommendable, to fasten all the electrodes by a single piece of ceramic material, as such a plate would become too heavy and would require reinforcing the supporting wires; besides the percentage of damaged pieces increases with the dimensions of ceramic plates. It is suitable to fasten the inner electrodes including the cathode by a ceramic body, as the active material sputtered from the cathode will not form a conducting surface as soon as on mica.

By fastening the electrodes in different planes and in separated spacers, the capacity between the both groups of electrodes and in particular between the control grid G1 and the anode A is considerably reduced. A further improvement is accomplished by inserting the metal shields S and S1 which are maintained at constant potential and preferably connected to the cathode. In this way the screen elements S and S1 do not need any additional fasteners, but form an uniform part with the insulating bodies. By dividing the electrodes in two groups, the electrodes including the supporting wires may be of different length. As it is seen from Fig. 1, the shielding effect of the screen grid G2 with regard to the control grid G1 is increased, as the path of the stray lines of force to the anode and the other electrodes situated beyond the screen grid is elongated.

Besides screening or reducing the stray capacity in multigrid tubes also maintenance of a good insulation and preventing surface leakage currents between the electrodes is of considerable importance. Although the construction described above is very advantageous in this re spect, additional improvements may be provided, tending to prolongation of the leakage path. For this purpose the holes, which accommodate the supporting wires may be conically widened and slots may be arranged between the holes.

In Fig. 3 one of the insulating discs or plates P2 is drawn on a large scale. The holes B1 to B5 are each formed with a central cylindrical portion to accommodate the electrode supporting wires while the opposite sides thereof are flared outwardly or conically widened. As it may be clearly seen, the leakage path is extended by this measure.

Fig. 4 illustrates one of the annular plates P1, wherein the circular holes B to B are provided in order to accommodate the wires supporting the electrodes G3, G4 and A. Between the holes B11 and B12 and B13 and B14 there are formed elongated slots 01 and 02, which are disposed in a direction perpendicular to the line joining the holes B11 to B14. Other cut-out portions 03 and 0 1 are provided between the holes B12 and B13 screens S and S1 respectively and the metal screen S.

I claim:

1. An electron discharge tube comprisingacathode, a cylindrical anode spaced from the cathode, a plurality of cylindrical grids surrounding the cathode and interposed in the space between said cathode and anode, a plurality of support rods for said electrodes excepting the cathode arranged parallel to the electrode axis, an annular disc of insulating material arranged transversely to the electrode axis and interconnecting the support rods of the anode and of certain of the grids, and a circular disc of insulating mate rial of substantially the size of the opening in the annular disc interconnecting the cathode and the support rods of the remaining grids.

2. An electron discharge tube according to claim 1 wherein said annular disc is made of mica and the circular disc of ceramic material.

3. An electron discharge tube according to claim 1 wherein said annular disc and said circular disc are wholly arranged in different parallel planes.

4. An electron discharge tube according to claim 1 wherein a pair of said annular and circular discs is provided at each end of the electrode support rods.

5. An electron discharge tube according to claim 1 wherein the discs of insulating material are provided with holes for accommodating the support rods, and at least one of said discs is provided with cut-out portions extending transversely between said holes.

6. An electron discharge tube according to claim 1 wherein the discs of insulating material are provided with holes for accommodating the support rods, and at least one of said discs is provided on its opposite faces with outwardly extending flares which are continuations of said holes.

7. An electron discharge tube comprising concentrically arranged cathode, control grid, screen grid and anode electrodes, and a cylindricallyshaped shield member radially spaced from and surrounding one end of the screen grid.

8. An electron discharge tube comprising concentrically arranged cathode, control grid, screen grid and anode electrodes, and a cylindricallyshaped shield member radially spaced from and surrounding each end of the screen grid.

9. An electron discharge tube comprising concentrically arranged cathode, control grid, screen grid and anode electrodes, and a cylindricallyshaped shield member radially spaced from and surrounding each end of the screen grid, said ring-shaped shield members being of suiiicient depth to extend for appreciable distances above and below the ends of the screen grid.

10. An electron discharge tube comprising a cathode, a control grid surrounding the cathode, screen grid and anode electrodes surrounding the control grid, a cylindrically-shaped shield member radially spaced from and surrounding the upper end of the screen grid and extending for an appreciable distance above and below that end, a leading-in conductor connected to the control grid at its upper end, and leading-in conductors connected to the remaining electrodes at their lower ends.

11. An electron discharge tube comprising a cathode, a control grid surrounding the cathode, screen grid and anode electrodes surrounding the control grid, a leading-in conductor connected to said control grid at one end, and means to shield the control grid and its leading-in conductor from electrostatic lines of force from the anode comprising a cylindrical shield member radially spaced from and surrounding that end of the screen grid which corresponds to the end oi the control grid having a connection to its leading-in conductor, said shield member being of sufiicient depth to extend for an appreciable distance above and below the end of the screen grid.

12. An electron discharge tube comprising a cathode, a control grid surrounding the cathode, screen grid and anode electrodes surrounding the control grid, a leading-in conductor connected to said control grid at one end, and means to shield the control grid and its leading-in conductor from electrostatic lines of force from the anode comprising an open-ended cylindrical shield member adapted to be maintained at cathode potential radially spaced from and surrounding that end of the screen grid which corresponds to the end of the control grid having a connection to its leading-in conductor, said shield member being of sufficient depth to extend for an appreciable distance above and below the end of the screen grid and provided at its upper edge with an outwardly flared portion.

13. An electron discharge tube comprising a cathode, an anode and a plurality of grid electrodes interposed between said cathode and anode, insulating means at one end of the electrode system for interconnecting the cathode and certain of the grid electrodes to maintain them in fixed spaced relation, separate insulating means at the same end of the system for interconnecting the anode and certain other of the grid electrodes. to maintain them in fixed spaced relation, and an open-ended cylindrical shield member interposed between said two insulating means.

i i. An electron discharge tube comprising a cathode, a cylindrical anode spaced from the cathode, a plurality of cylindrical grids surrounding the cathode and interposed in the space between said cathode and anode, a plurality of support rods for said electrodes excepting the cathode arranged parallel to the electrode axis, an annular disc of insulating material arranged transversely to the electrode axis and interconnecting the support rods of the anode and of certain of the grids, a circular disc of insulating material of substantially the size of the opening in the annular disc interconnecting the cathode and the support rods of the remaining grids, and a short cylindrically shaped shield member interposed between said annular and circular discs and extending for an appreciable distance into the space between adjacent grids.

KARL STEIMEL. 

